The present invention relates to a sensor for producing one or more electrical signals which are proportional to the spectral content of electromagnetic energy incident upon the sensor. More specifically, the present invention relates to a sensor and processor for controlling the headlights or passenger heating and cooling system of a vehicle in response to ambient light conditions.
Many automobile drivers prefer that certain systems be adjusted automatically based upon weather and ambient light conditions. For example, when driving at night, in rain, or through a tunnel, drivers prefer headlights to be illuminated. Artificial lighting in a tunnel or headlights on other vehicles preferably do not defeat the automatic illumination of headlights under those conditions. Bright sunlight, however, might indicate that full-strength headlight illumination is unnecessary.
In prior systems for distinguishing between natural and artificial light, filters have been used to pass light from two different portions of the visible spectrum (or from a narrow band and a broad band of the visible spectrum) to two identical photodiodes that respond to the total amount of light reaching their surface. When filters are used, however, the light energy reaching the photodiode is substantially attenuated. This makes the circuit more susceptible to noise in the photodiode output signal.
Another prior system for distinguishing between natural and artificial light focuses unfiltered light on one photodiode while focusing light through a blue filter onto a second photodiode. To compare the photodiode outputs, the signal responsive to the blue-filtered light must be normalized prior to the comparison. Again, this normalization makes the system more sensitive to noise in the second photodiode.
While these and other prior systems attempt to match sensor response to the objective response of the human eye to visible light, it has been discovered that the subjective response of many drivers to ambient light also depends upon the amount and spectral content of light received that lies outside the visible spectrum. For example, drivers feel cooler on overcast days than on sunny days.
It is an object of the present invention to provide an improved ambient light sensor.
It is yet another object of the present invention to provide an ambient light sensor which is capable of more accurately distinguishing between natural and artificial ambient light.
These objects and others have been achieved through the design of a vehicle system controller that uses photosensors with different peak response frequencies to distinguish between ambient natural and artificial light. In one embodiment, the peak response from one photodiode occurs in the visible spectrum, while the peak response from another photodiode occurs in the infrared spectrum.
In some embodiments, an anti-reflective coating is used on at least a portion of one photodiode.
In some embodiments, the controller turns the vehicle headlights on (or leaves them on) in spite of substantial artificial light in a tunnel. In some embodiments, the controller turns the vehicle headlights on (or leaves them on) in spite of receiving substantial artificial light from another vehicle.
In some embodiments, the controller operates an environmental control system (for example, for heating and cooling the vehicle) based at least in part on the quantity and/or type of ambient light received.